Data networks are known from the prior art. It is known that data networks can be created in different topologies, for example in a ring topology or in an open ring topology (line topology).
Cable-connected data networks according to the prior art are frequently based on the Ethernet standard. Ethernet data networks can be operated in the prior art at different transmission rates, for example at transmission rates of 10 Mbit/s, 100 Mbit/s or 1 Gbit/s.
Under the generic term of “Industrial Ethernet,” it is furthermore known in the prior art to use Ethernet data networks for the networking of devices in industrial manufacturing and automation technology. Data networks of this type may be based, for example, on the EtherCAT standard according to the IEC standard “IEC 61158.”
Ethernet controllers which support a transmission rate of 1 Gbit/s can normally also be operated at 100 Mbit/s. If a network comprises some network participants which support transmission rates of 1 Gbit/s and 100 Mbit/s, and other network participants which support 100 Mbit/s only, the complete network should be operated at 100 Mbit/s.
The highest possible transmission rate can be set, for example automatically, between two adjacent network participants of a network. If two adjacent network participants both support 1 Gbit/s, a connection is established between these network participants on activation with a transmission rate of 1 Gbit/s. In order to change this connection to a transmission rate of 100 Mbit/s, the connection must be cleared down and then re-established with a transmission rate of 100 Mbit/s. This procedure takes a relatively long time of around 1 s.
If, in an example of a network with a line topology, a first network participant disposed at one end supports a transmission rate of 100 Mbit/s only, whereas all other network participants also support a transmission rate of 1 Gbit/s, the connections of the first network participant are initially established with a transmission rate of 100 Mbit/s, whereas the remaining connections of the network are established with a transmission rate of 1 Gbit/s.
A second network participant adjacent to the first network participant then recognizes that one of its connections is set to a transmission rate of 100 Mbit/s, whereas another of its connections is set to a transmission rate of 1 Gbit/s and must therefore be converted. To do this, the second network participant clears down this connection and re-establishes it with a transmission rate of 100 Mbit/s, which takes the aforementioned time of around 1 s. A third network participant adjacent to the second network participant then recognizes that one of its connections is now set to a transmission rate of 100 Mbit/s, whereas another of its connections is set to a transmission rate of 1 Gbit/s. This connection is in turn cleared down and re-established, which again takes the aforementioned time.
In this way, the speed adaptation propagates gradually through the network. The transmission rates are not converted simultaneously, but successively for each connection individually. A long time passes here until the network is ready for operation.